The present invention relates to a motor speed control and, more particularly, to a motor speed control which is applicable to an optical disk apparatus and others.
A motor speed control is adapted to control the speed of a motor to a predetermined object speed. In a motor speed control known in the art, a frequency proportional to an object speed and a frequency proportional to a real speed detected are converted into voltages by individual frequency-to-voltage converters, so that a difference between the object and real speeds is determined based on the difference between the two voltages. Such a difference in speed is added to a difference in phase between the object and real speeds so as to control the motor to the object speed based on the sum. However, the prior art motor speed control has a problem which is ascribable to the non-linearity, scattering in conversion ratio and others of the frequency-to-voltage converters. Specifically, even when the object and real speeds are equal to each other, a difference is developed between the outputs of those converters resulting in detection errors.